Microstructure and high-temperature mechanical properties of near net shaped Ti−45Al−7Nb−0.3W alloy by hot isostatic pressing process

Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that at a temperature of 700℃,the peak yield stress(YS)and ultimate tensile stress(UTS)of alloy are 534 and 575 MPa,respectively,and the alloy shows satisfactory comprehensive mechanical properties at 850℃.The alloy exhibits superplastic characteristics at 1000℃ with an initial strain rate of 5×10^−5 s^−1.When the tensile temperature is below 750℃,the deformation mechanisms are dislocation movements and mechanical twinning.Increasing the tensile temperature above 800℃,grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.

Fabrication of Near Net Shape Metallic Foam via Plaster Mould

Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefits （i.e. reduce the unit cost of goods and fabrication process etc.） to fabrication of metallic foams. In this article, the fabrication characteristic of near net-shape metallic foams by direct foaming method was evaluated. Al and Plaster was used for base material and mould material respectively. Ca and TiH2 were added to molten Al as thickening and blowing agent for stable condition of bubbles. Thickening time was about 10 min with a stirring speed of 600 r/min. Foaming time was 30-120 s for evaluation of the optimum foaming condition. Amount of agent was selected by pre-experimental data. Porosity of near net-shape goods was measured by Archimedes method. On the other hand, it seems that increasing poring time and thickening agent make the poor porosity

Determining casting defects in near-net shape casting aluminum parts by computed tomography

Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting （Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy）, die casting （A356, A1-7Si-0.3Mg）, and semi-solid casting （A356, A1-TSi-0.3Mg）, respectively. Unlike die casting （second part）, low-pressure die casting （first part） sig- nificantly reduced the formation of casting defects （i.e., porosity） due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi- solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.

A Novel near Net-Shape Technique for P/M Parts with Large H/D Ratio

In order to overcome the shortcomings of conventional hot pressing, a novel near net-shape technique, called radial hot pressing, for P/M parts with large height-to-diameter (H/D) ratio was introduced. Effects of processing parameters on the microstructures and density of P/M TiAl base alloy valves were studied. Results show that the radial hot pressing is an effective technique for manufacturing valves with a H/D ratio of about 10:1, and the perfect joint interface between the Mo sheet and the parts is helpful for subsequent HIPing.

基于C#.NET的贴边钢岔管设计的CAD系统开发与应用

针对水电站贴边钢岔管设计繁琐、工作量大等缺点,开发出了其计算机辅助设计系统。该系统实现了网格智能划分,并能人性化多项指标自由加密网格,生成ANSYS命令流与有限元软件对接;能够在完全独立于CAD系统之外设计,生成DXF文件与CAD软件对接;采用了三种功能模块分离的设计构架,同时采用了子父窗体设计,支持多模型任务同时运算等。最后运用该软件对招徕河水电站工程实例进行了分析,结果表明本系统具有设计速度快,精度高,实用性强等优点,能大大减小贴边岔管手工计算的工作量。

复杂异形窗体在VB.NET中的设计与实现

以VB.NET为开发平台,讨论了开发异形窗体的基本原理和方法,并给出了一个实例;还论述了实现复杂异形窗体的一些改进措施及扩展补充方法。

基于改进U-Net的白细胞提取方法研究

目的:提出一种基于改进U-Net的白细胞提取方法,以解决从血涂片图像中提取白细胞时白细胞粘连和尺寸影响提取精度的问题。方法:在常规U-Net中增加一个形状特征提取层,通过卷积得到细胞的宽度、高度、面积、数量等形状相关信息,并将形状信息引入到损失函数中,从而实现对不同大小的细胞和粘连细胞的有效分割。细胞分割完成后,对分割得到的二值图像进行连通区域提取得到每个白细胞的矩形框区域,从而实现血涂片图像中白细胞的提取。将该方法与U-Net、Faster R-CNN进行对比以验证其提取白细胞的效果。结果:该方法的提取精度(F_(1)值)达到99.20%,较U-Net、Faster R-CNN分别提高了0.80%、2.19%。结论:该方法对粘连细胞及不同大小的白细胞均有很好的提取效果,能够满足白细胞识别分类需求。

Additive Manufacturing of Ceramic Structures by Laser Engineered Net Shaping

Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this problem, direct fabrication of Al2O3 ceramic structures is conducted by laser engineered net shaping system and pure ceramic powders. Grain refinement strengthening method by doping Zr O2 and dispersion strengthening method by doping Si C are proposed to suppress cracks in fabricating Al2O3 structure. Phase compositions, microstructures as well as mechanical properties of fabricated specimens are then analyzed. The results show that the proposed two methods are effective in suppressing cracks and structures of single-bead wall, arc and cylinder ring are successfully deposited. Stable phase of α-Al2O3 and t-Zr O2 are obtained in the fabricated specimens. Micro-hardness higher than 1700 HV are also achieved for both Al2O3 and Al2O3/Zr O2, which are resulted from fine directional crystals generated by the melting-solidification process. Results presented indicate that additive manufacturing is a very attractive technique for the production of high-performance ceramic structures in a single step.

Comparison of Drags on Fish Cages of Different Shapes

The effects of the direction of current on the drag on fish cages are studied in the present paper. The drags on cages of different shapes, including cylindrical, tnmcated conical, cuboidal and hexagonal, are compared. The drag on the tnmcated conical net is smaller than that on other shapes of the same area. This net shape with a small apex angle is suggested for the design of fish cages.

Laser engineered net shaping of Co-based superalloys

Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.

.NET环境下基于UG journal的异型辊设计模块二次开发

在分析UG/Open API二次开发方法不足之处的基础上,运用UG NX软件的NX Open For.NET与UGJournal功能,在.NET平台下用C#语言对机车梁矫直机异型辊参数化设计模块进行二次开发,对NX全新的开发方法进行了详细说明。

基于改进U-Net的人脑黑质致密部分割

人脑黑质致密部分割能够为帕金森病的诊断提供一定依据。黑质致密部在人脑核磁共振成像中像素占比低、类间差异小,为提高计算机辅助诊断系统对人脑黑质致密部的分割精度,提出一种基于改进U形神经网络(U-Net)的人脑黑质致密部分割方法。为了提取更多有效的多尺度图像语义特征,结合U-Net的跨连接结构并采用多头注意力机制,同时融合基于Transformer编码器的高维语义编码模块以提取高维语义特征,避免浅层噪声对特征造成的影响。建立多任务模型并设计基于二维高斯核权重掩膜的损失函数,解决神经网络分割模型因多次下采样造成的不连续分割误差问题。构建包括140个帕金森病患者以及48个健康对照者的高精度核磁共振脑成像数据集进行实验,结果表明,相较常用的医疗影像分割方法 R2U-Net、HANet等,该方法的多任务分割效果取得明显提升,戴斯相关系数和AUC指标分别达到0.869 1和0.943 9,消融实验结果也验证了改进编码器和改进损失这2个模块的有效性。

粉末近净成形在航天发动机领域的应用

粉末近净成形(Powder metallurgy near net shaping,PM-NNS)技术能够制备出具有优异综合力学性能的粉末合金复杂部件。介绍了粉末热等静压(Hot isostatic pressing,HIP)近净成形技术原理及优势,综述了近年来国内外粉末近净成形在航天发动机领域的研究现状,从工艺路线和构件研制两方面展开,简述了构件制备过程的影响因素及缺陷控制,结合中国科学院金属研究所粉末近净成形技术在航天发动机领域的研究及应用情况,总结了粉末近净成形技术当前存在的主要问题及发展方向,以期进一步拓宽该技术的应用范围。

Ti_(2)AlNb合金粉末热等静压成形的组织和性能

分别采用等离子旋转电极雾化法(Plasma rotating electrode process,PREP)和无坩埚感应熔炼超声气体雾化法(Electrode induction melting gas atomization,EIGA)制备了Ti_(2)AlNb洁净预合金粉末,并对预合金粉末进行了表征。通过热等静压(Hot isostatic pressing,HIP)工艺制备了Ti_(2)AlNb合金,研究了制粉工艺对Ti_(2)AlNb合金显微组织与力学性能的影响。试验结果表明,与PREP法相比,EIGA法制备的Ti_(2)AlNb粉末振实密度更高;基于粉末热等静压近净成形技术,在1030℃/140 MPa/3 h的条件下开展了Ti_(2)AlNb叶轮的成形研究,有限元模拟结果显示,粉末振实密度越高,部件热等静压后变形程度越小,综合考虑构件成形,优选振实密度更高的EIGA制粉工艺制备Ti_(2)AlNb粉末合金复杂部件。

BEST LIPSCHITZ CONSTANTS FOR THE BEZIER NETS AND BERNSTEIN POLYNOMIALS OVER A SIMPLEX

The present paper finds out that the geometric entity which characterizes the best Lipschitz constants for the Bezier nets and Bernstein polynomials over a simplex sigma is an angle Phi determined by sigma, and proves that (1) if f(x) is Lipschitz continuous over sigma, i.e., f(x) is an element of Lip(A)(alpha,sigma), then both the n-th Bezier net <(f)over cap (n)> and the n-th Bernstein polynomial B-n(f;x) corresponding to f(x) belong to Lip(B)(alpha,sigma) , where B = Asec(alpha)Phi; and (2) if n-th Bezier net <(f)over cap (n)> is an element of Lip(A)(alpha,sigma), then the elevation Bezier net <E(f)over cap (n)> and the corresponding Bernstein polynomial. B-n(f,;x) also belong to Lip(A)(alpha,sigma). Furthermore, the constant B = Asec(alpha)Phi, in case (1) is best in some sense.

梨简化树形及树体改造技术

以鄂梨2号为试验材料,研究棚架改造树形、改良纺锤形及小冠疏层形的冠层相对光照强度、叶片光合效率及其对果实品质、田间产量的影响。结果表明,棚架改造树形、改良纺锤形、小冠疏层形的冠内平均相对光照强度分别为71.58%、72.78%、50.96%,小冠疏层形存在无效光区;叶片平均净光合速率分别为11.56、11.39、8.08μmol CO_(2)/(m^(2)·s)。棚架改造树形果实单果质量、可溶性固形物含量分别较小冠疏层形高17.59%、6.61%;改良纺锤形的田间产量较棚架改造树形高47.80%,小冠疏层形的田间产量较棚架改造树形高11.90%,存在显著差异。鄂梨2号的棚架改造树形及改良纺锤形显著改善了树体的风、光通透条件,叶片光合效率高,为提升果实品质及增加田间产量打下了物质基础。

颗粒增强铝基复合材料热等静压近净成形有限元模拟

目的建立可靠的模拟方法,以更高效地预测颗粒增强铝基复合材料(PRAMC)粉末热等静压中的形状变化和不同部位致密度的差异,解决传统实验试错方法适用性差且费时费力的问题,满足批量应用的需求。方法以45%(体积分数)SiCp/6092Al复合材料为研究对象,构建了能预测粉末热等静压成形过程的有限元模型。使用Gurson-Tvergard-Needleman(GTN)模型作为粉末本构模型,建立了粉末尺度的代表性体积单元(RVE)对GTN模型进行修正。结果通过对比GTN模型计算结果与实验结果,发现修正后的GTN模型能更准确地预测模型的最终变形尺寸,与修正前相比,相对误差降低了1.6%~2.9%。使用修正后的GTN模型对杯形回转体零件的热等静压成形过程进行预测,最终形状的计算结果与实验结果的相对误差仅为0.2%~3.1%,致密度分布的相对误差在0.5%以内。在探究包套厚度对热等静压过程的影响时发现,随着包套厚度的增大,热等静压过程中的屏蔽作用增强,内部粉体致密度下降。结论为PRAMC热等静压近终形制备的形状和致密度控制问题提供了有限元预测工具,辅助优化了热等静压工艺和包套设计,降低了颗粒增强铝基复合材料热等静压近净成形过程开发的试错成本。

西安国际足球中心索网结构缩尺模型静载试验研究

为了研究索网结构静力荷载下的内力和变形特点,按照1∶10比例设计制作了西安国际足球中心的缩尺模型试件,采用新型空间结构水重力点阵加载系统逐级控制加载,以及DACS-Measure现场测量系统,分别对该模型上半跨、右半跨及全跨进行了分级静力加载试验。试验结果表明:新型空间结构点阵自动同步加载系统能实现任意比例、多点同步精确加载,普遍适用于各类空间结构加载试验;在不同加载模式下,索网竖向变形随荷载增加均基本呈现线性变化,且最大变形发生在索网洞口边缘处;上半跨荷载、右半跨荷载及全跨荷载下索力最大位置均位于索网中轴偏右位置处。研究成果可为我国以后此类索网结构的加工制造及施工应用提供技术参考。

基于多神经网络的可展开网状天线型面调整方法

为在提高可展开网状天线型面精度的同时减少型面调整的工作量,提出了一种基于多神经网络的型面调整方法。通过分析新型张拉网状天线型面与调整索相关性与耦合机制,首次提出了型面调整策略。以10m口径的新型张拉网状天线为例进行了数值仿真研究,调整后型面的均方根值从5.4×10^(-3)m降低到1.1×10^(-3)m,从而验证了方法的有效性。

3D打印技术在车身车间的应用分析

随着汽车行业竞争的日益加剧,汽车制造成本需要不断优化、制造周期也在不断地压缩优化。因此,具有高效加工能力、节约成本及轻量化特点的3D打印技术在汽车制造中被越来越多地应用和推广。文章主要对非金属3D打印技术在车身车间生产制造中的应用场景进行了研究,并对其应用特点进行了分析,从而为汽车制造中车身车间3D打印技术的应用开发提供参考。